Utilized is an information processing apparatus called an Input Output server (which will hereinafter be simply termed the IO server) for providing services as a file system or DBMS (Database Management System) and other equivalent systems, the server including an external storage device instanced by a disk device and other equivalent storages. A decrease in unit price of capacity of the external storage device in recent years facilitates adopting a high-level measure against a failure of the external storage device itself due to, e.g., multiplexing or RAID (Redundant Arrays of Inexpensive Disks) or other equivalent configurations.